Paperboard containers (e.g., drinking cups) are typically formed with a generally conically-shaped tubular side wall and a bottom wall. The bottom wall is joined to the side wall by gluing and by rolling or curling a bottom rim of the side wall over the bottom wall so that the side and bottom walls form a substantially liquid tight (i.e., leak-proof) annular seam.
As may be appreciated, this curling of the bottom rim of the container side wall is a stressful operation on the paperboard. That is, curling of the bottom rim can cause damage to occur to printed indicia or protective coatings that may be on the side wall resulting in the manufacture of a container which is not suitable for commercial sale. To overcome this problem, it has been conventional practice to lubricate the bottom of the container before curling with a food-grade lubricating mineral oil using a spray tool. The lubricated container bottom is then brought into contact with a rotating curling tool.
However, spraying of the lubricant onto the container bottom has several disadvantages such as contaminating the container-forming equipment and other containers with overspray as well as applying excessive amounts of the lubricant to the containers (which could damage the appearance of the finished container product). Moreover, use of a high speed rotating curling tool has the disadvantage of generating excessive heat which could damage the container (e.g., coatings applied to the container side wall).
It would therefore be especially desirable if the bottom side wall rim of a paperboard container could be concurrently lubricated and curled without using spray techniques or a rotating curling tool. It is towards fulfilling such needs that the present invention is directed.
Broadly, therefore, the present invention is embodied in apparatus and method for concurrently lubricating and curling a rim of a paperboard container. The preferred embodiment of the rim lubricating and curling apparatus includes a housing block defining a central recess sized and configured to accept therein a rim of a paperboard container to be curled. An annular curling channel is disposed in the recess for curling the rim of the paperboard container in response to relative advancing movement between the paperboard container and the housing block. The housing block also defines an annular liquid channel concentrically disposed in surrounding relationship to the annular curling channel for distributing lubricating liquid. A porous liquid transfer ring is attached to the housing block in covering relationship to the annular liquid channel so that lubricating liquid supplied to the liquid channel comes into wiping contact with the liquid transfer ring.
The liquid transfer ring includes a circular edge surface which defines a central opening which is sized such that the liquid transfer ring extends at least partially over the curling channel. In use, the rim of the paperboard container comes into wiping contact with the central opening of the liquid transfer ring so that lubricating liquid is transferred thereto prior to the rim being curled in the curling channel.
Further aspects and advantages of this invention will become more clear after careful consideration is given to the detailed description of the preferred exemplary embodiments thereof which follows.